Isaac Leffler (November 7, 1788 – March 8, 1866), sometimes spelled Lefler or Loeffler, was an American lawyer and Iowa pioneer who represented Virginia's 18th congressional district in the United States House of Representatives for one term in the 1820s. He also served in the legislatures of the Commonwealth of Virginia, as well as the Wisconsin and Iowa Territories. His younger brother, Shepherd Leffler, became one of Iowa's first congressmen after achieving statehood.